CN107949436B

CN107949436B - Integrated SCR and ammonia oxidation catalyst system

Info

Publication number: CN107949436B
Application number: CN201680050901.9A
Authority: CN
Inventors: M·希尔真多夫; K·杜穆布亚; C·赞贝尔; S·斯蒂贝尔斯
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2015-09-04
Filing date: 2016-08-29
Publication date: 2021-11-12
Anticipated expiration: 2036-08-29
Also published as: RU2018111984A; RU2018111984A3; US20190022584A1; WO2017037006A1; US11213789B2; CN107949436A; KR20180050687A; JP6885927B2; JP2018534126A; EP3344384A1; KR102593060B1; MX2018002701A; CA2997040A1

Abstract

A catalyst is described comprising a washcoat containing copper or iron on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms physically mixed with platinum and rhodium on a refractory metal oxide support comprising alumina, silica, zirconia, titania, physical mixtures thereof, or chemical combinations including atom doping combinations. The invention also describes a catalyst comprising: a first washcoat zone containing copper or iron on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms, the first washcoat zone being substantially free of platinum group metals; and a second washcoat zone containing copper or iron on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms physically mixed with platinum and rhodium on a refractory metal oxide support comprising alumina, silica, zirconia, titania, physical mixtures thereof, or chemical combinations including atom doping combinations. Methods and systems for treating emissions are also described.

Description

Integrated SCR and ammonia oxidation catalyst system

Technical Field

The present invention relates to catalysts, methods of treating emissions in exhaust gas streams, and systems for treating emissions produced in exhaust gas streams.

Background

The diesel engine discharges asA heterogeneous mixture comprising particulate emissions such as soot and gaseous emissions such as carbon monoxide, unburned or partially burned hydrocarbons and nitrogen oxides (collectively referred to as NO)_x). Catalyst compositions, typically disposed on one or more monolithic substrates, are placed in engine exhaust systems to convert some or all of these exhaust components to harmless compounds.

Ammonia Selective Catalytic Reduction (SCR) is a NO used to meet diesel and lean burn engine requirements_xEmission of targeted NO_xAnd (3) emission reduction technology. In an ammonia SCR process, NO is made_x(usually by NO + NO)₂Composition) with ammonia (or an ammonia precursor such as urea) over a catalyst, typically composed of a base metal, to form dinitrogen (N)₂). This technology enables NO in a typical diesel engine drive cycle_xThe conversion is greater than 90%, so it represents the achievement of positive NO_xOne of the most preferred ways to reduce emissions targets.

A characteristic feature of some ammonia SCR catalyst materials is the tendency to retain significant amounts of ammonia at the Lewis and Bronsted acid sites on the catalyst surface during the low temperature portion of a typical drive cycle. The subsequent increase in exhaust temperature may cause ammonia to desorb from the ammonia SCR catalyst surface and exit the exhaust pipe of the vehicle. Ammonia metering in excess to increase NO_xConversion is another potential situation where ammonia may be emitted from an ammonia SCR catalyst.

Ammonia slip from ammonia SCR catalysts presents a number of problems. NH (NH)₃Has an odor threshold of 20ppm in air. Eye and throat irritation was detectable above 100ppm, skin irritation occurred above 400ppm, and IDLH was 500ppm in air. NH (NH)₃Are corrosive, especially in their aqueous form. In the cooler region of the exhaust line downstream of the exhaust catalyst, NH₃And condensation of water will produce a corrosive mixture.

Therefore, it is desirable to eliminate ammonia before it enters the tailpipe. For this purpose, a selective ammonia oxidation (AMOx) catalyst is used, the purpose of which is to convert excess ammonia to N₂。

WO 2010/062730 describes the use of a primer coating comprising Pt on alumina located at the outlet region of the monolith, wherein the copper coating on the chabazite is distributed over the entire length of the monolithic converter.

Despite the use of selective ammonia oxidation catalysts, it would be desirable to provide a catalyst for selective ammonia oxidation that is capable of converting ammonia over a wide range of temperatures in vehicle drive cycles where there is ammonia slip and that produces a minimal amount of nitrogen oxide by-product. AMOx catalyst should also produce a minimum amount of N₂O, a potential greenhouse gas.

SUMMARY

Aspects of the invention include catalyst systems for treating exhaust gas streams and methods of preparing catalysts for treating the gases. The term "catalyst system" as used herein shall include two or more chemical catalytic functions on one substrate or on more than one separate substrate.

A first aspect of the invention relates to a catalyst for oxidizing ammonia. In a first embodiment, a catalyst for oxidizing ammonia comprises: a washcoat containing copper or iron on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms mixed with platinum and rhodium on a refractory metal oxide support including alumina, silica, zirconia, titania, physical mixtures thereof or chemical combinations including atom doping combinations.

In a second embodiment, the catalyst of the first embodiment is adapted wherein the washcoat is disposed on a monolithic substrate.

In a third embodiment, the catalyst of the second embodiment is adapted, wherein the monolithic substrate is a flow-through honeycomb substrate comprising a plurality of fine, substantially parallel gas flow channels extending along the longitudinal axis of the substrate.

In a fourth embodiment, the catalyst of the first through third embodiments is adapted, wherein the catalyst comprises an amount of platinum and an amount of rhodium.

In a fifth embodiment, the catalyst of the fourth embodiment is modified wherein the amount of platinum is in the range of 0.3 to 20g/ft³Is present in an amount of 0.3 to 20g/ft³Is present and wherein no other platinum group metals are present.

In a sixth embodiment, the catalyst of the first through fifth embodiments is adapted wherein the copper or iron on the molecular sieve material and the platinum and rhodium on the refractory metal oxide support are homogeneously mixed in the washcoat.

In a seventh embodiment, the catalyst of the first through fifth embodiments is adapted wherein the copper or iron on the molecular sieve material and the platinum and rhodium on the refractory metal oxide support are separated from each other and the platinum and rhodium on the refractory metal oxide support is physically mixed with the copper or iron on the molecular sieve material.

In an eighth embodiment, the catalyst of the first through seventh embodiments is adapted wherein the refractory metal oxide support is doped with one or more dopants selected from the group consisting of Ce, La, Ba, Zr, Hf, Ta, Mn, Si, Ti, W, Mo, and Re.

In a ninth embodiment, the catalyst of the first through eighth embodiments is modified wherein the washcoat is substantially free of copper aluminate.

In a tenth embodiment, the catalyst of the first through ninth embodiments is adapted wherein the molecular sieve material is selected from the group consisting of framework types CHA, AEI, AFX, ERI, KFI, LEV, AFT, EAB, DDR, PAU, RHO, SAV, SAT, TSC, UEI, and combinations thereof.

In an eleventh embodiment, the catalyst of the first through tenth embodiments is adapted, wherein the molecular sieve material has a CHA framework type.

In a twelfth embodiment, the catalyst of the first through ninth embodiments is adapted wherein the molecular sieve material has a silica to alumina ratio of from 2 to 200.

In a thirteenth embodiment, the catalyst of the first through twelfth embodiments is adapted wherein the washcoat comprises copper on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms.

In a fourteenth embodiment, the catalyst of the first through twelfth embodiments is modified, wherein the washcoat comprises iron on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms.

A second aspect of the invention relates to a catalyst for oxidizing ammonia. In a fifteenth embodiment, a catalyst for oxidizing ammonia comprises: a first washcoat zone comprising copper or iron on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms, wherein the first washcoat zone is substantially free of platinum group metals; and a second washcoat zone comprising copper or iron on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms physically mixed with platinum on a refractory metal oxide support comprising alumina, silica, zirconia, titania, physical mixtures thereof, or chemical combinations including atom doping combinations.

In a sixteenth embodiment, the catalyst of the fifteenth embodiment is adapted, wherein the first washcoat zone and the second washcoat zone are disposed on a monolithic substrate.

In a seventeenth embodiment, the catalyst of the sixteenth embodiment is modified, wherein the first washcoat zone and the second washcoat zone are adjacently disposed on a monolithic substrate, and the first washcoat zone is located upstream of the second washcoat zone.

In an eighteenth embodiment, the catalyst of the fifteenth to seventeenth embodiments is modified, wherein the second washcoat region comprises platinum and no other platinum group metals.

In a nineteenth embodiment, the catalyst of the fifteenth to seventeenth embodiments is modified, wherein the second washcoat region further comprises rhodium and no other platinum group metals.

In a twentieth embodiment, the catalyst of the fifteenth to nineteenth embodiments is adapted, wherein the molecular sieve material is selected from the group consisting of framework types CHA, AEI, AFX, ERI, KFI, LEV, AFT, EAB, DDR, PAU, RHO, SAV, SAT, TSC, UEI, and combinations thereof.

In a twenty-first embodiment, the catalyst of the fifteenth to twentieth embodiments is adapted, wherein the molecular sieve material has a CHA framework type.

In a twenty-second embodiment, the catalyst of the fifteenth to twenty-first embodiments is modified, wherein the molecular sieve material has a silica to alumina ratio of from 2 to 200.

A third aspect of the invention relates to a method for treating emissions. In a twenty-third embodiment, a method for treating emissions produced in an exhaust stream of a lean burn engine comprises: injection of ammonia or ammonia precursor into a gas containing NO_xCO or hydrocarbons; and passing the exhaust stream over the catalyst of any one of the first to twenty-second embodiments.

A fourth aspect of the invention is directed to a system for treating emissions. In a twenty-fourth embodiment, a system for treating emissions produced in an exhaust stream of a lean burn engine comprises: an ammonia source and an injector for injecting the ammonia source into the exhaust stream; a selective catalytic reduction catalyst downstream of the ammonia source to promote the reaction of ammonia with nitrogen oxides to selectively form nitrogen and H₂O; and a catalyst according to any one of the first to twenty-second embodiments.

In a twenty-fifth embodiment, the system of the twenty-fourth embodiment is modified, wherein the system further comprises an ammonia oxidation (AMOx) catalyst.

Brief Description of Drawings

The following figures illustrate embodiments of the invention. It should be understood that the figures are not to scale and that certain features, such as monolith channels, may be increased in size to show features according to embodiments of the invention.

FIG. 1 shows a partial cross-sectional view of a catalyst according to one or more embodiments;

FIG. 2A shows a partial cross-sectional view of a catalyst according to one or more embodiments;

FIG. 2B shows a partial cross-sectional view of a catalyst according to one or more embodiments;

FIG. 3A shows a perspective view of a wall-flow filter substrate;

FIG. 3B shows a cross-sectional view of a second wall-flow filter substrate; and

FIG. 4 is a schematic illustration of an engine emissions treatment system according to one or more embodiments. Detailed description of the invention

Before describing several exemplary embodiments of the invention, it is to be understood that the invention is not limited to the details of construction or process steps set forth in the following description. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

Embodiments of the present invention relate to catalysts for oxidizing ammonia. A first aspect of the invention is directed to a catalyst comprising a washcoat containing copper or iron on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms mixed with platinum and rhodium on a refractory metal oxide support. A second aspect of the invention relates to a catalyst comprising: a first washcoat zone containing copper or iron on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms and a second washcoat zone containing copper or iron on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms mixed with platinum on a refractory metal oxide support.

It has surprisingly been found that the catalyst is particularly suitable for use in exhaust gas purification catalyst assemblies, in particular as providing good NO_xConversion and low N₂O and NH₃An ammonia oxidation catalyst in the amount discharged. During the temperature increase (i.e. from about 200 ℃ to 300 ℃ and 400 ℃) accompanied by a strong decrease in the ammonia adsorption capacity, it is desirable to avoid NH₃And (5) discharging.

With respect to the terms used in this disclosure, the following definitions are provided.

As used in this specification and the appended claims, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a catalyst" includes mixtures of two or more catalysts, and the like.

As used herein, the term "emission reduction (abate)" means a reduction in quantity, and "emission reduction (abatment)" means a reduction in quantity caused by any means. The terms "exhaust stream" and "engine exhaust stream," if present herein, refer to engine outlet effluent as well as effluent downstream of one or more other catalyst system components (including, but not limited to, diesel oxidation catalysts and/or soot filters).

One aspect of the present invention relates to a catalyst. According to one or more embodiments, the catalyst may be disposed as a washcoat on a monolithic substrate. As used herein and as described in Heck, Ronald and Robert Farrauto, Catalytic Air Pollution Control, New York: Wiley-Interscience, 2002, pages 18-19, the washcoat comprises compositionally different layers of material disposed on the surface of or underlying the monolithic substrate. The washcoat is typically composed of a high surface area support (e.g., alumina) and a catalytic component (e.g., a platinum group metal). The catalyst may comprise one or more washcoat layers, and each washcoat layer may have a unique chemical catalytic function.

The term "catalyst" or "catalyst composition" or "catalyst material" as used herein refers to a material that promotes a reaction.

The term "catalytic article" as used herein refers to a component used to promote a desired reaction. For example, the catalytic article may comprise a washcoat containing catalytic species (e.g., catalyst composition) on a substrate.

As used herein, the term "selective catalytic reduction" (SCR) refers to the reduction of nitrogen oxides to dinitrogen (N) using a nitrogenous reductant₂) The catalytic process of (1).

The selective reduction process is referred to as the SCR process (selective catalytic reduction). The SCR process uses the catalytic reduction of nitrogen oxides with ammonia in the presence of atmospheric oxygen, mainly forming nitrogen and steam:

4NO+4NH₃+O₂→4N₂+6H₂o (Standard SCR reaction)

2NO₂+4NH₃→3N₂+6H₂O (Slow SCR reaction)

NO+NO₂+NH₃→2N₂+3H₂O (Rapid SCR reaction)

Ideally, the catalyst used in the SCR process should be able to maintain good catalytic activity under hydrothermal conditions over a wide range of service temperature conditions (e.g., 200 ℃ or greater). In practice, hydrothermal conditions are often encountered, for example, during regeneration of soot filters, components of exhaust gas treatment systems for removing particulates.

The term "NH₃The oxidation reaction "or" ammoxidation reaction "is used herein to refer to a chemical process described by:

4NH₃+5O₂→4NO+6H₂O(NH₃oxidation reaction)

More generally, the term "NH₃The oxidation reaction "means ammonia (NH)₃) With oxygen (O)₂) React to produce NO, NO₂、N₂O or preferably N₂The process of (1). The term "NH₃Oxidizing composition "means an effective catalyst for NH₃A material composition for oxidation reaction.

SCR compositions

According to one or more embodiments of the invention, as NO_xA portion of the abatement catalyst composition employs a component in the washcoat that is effective to catalyze the SCR function (referred to herein as the "SCR component"). Typically, the SCR component is part of a composition that includes other components in the washcoat. However, in one or more embodiments, NO_xThe abatement catalyst composition may comprise the SCR component alone.

The phrase "molecular sieve" as used herein refers to framework materials, such as zeolites and other framework materials (e.g., crystallographically substituted materials), that can be used as catalysts in particulate form in combination with one or more promoter metals. Molecular sieves are materials based on extensive three-dimensional networks of oxygen ions, which typically contain tetrahedral sites and have a substantially uniform pore distribution with an average pore size no greater than 20 angstroms. The pore size is determined by the ring size. The term "zeolite" as used herein refers to a specific example of a molecular sieve that contains silicon and aluminum atoms. In accordance with one or more embodiments, it will be understood that the molecular sieve is defined by its framework type, and is intended to include framework types as well as any and all homogeneous framework materials, such as SAPO, ALPO, and MeAPO materials having the same framework type, as the zeolitic material.

In a more specific embodiment, reference to an aluminosilicate zeolite framework type limits the material to molecular sieves that do not include substituted phosphorus or other metals in the framework. However, for clarity, as used herein, "aluminosilicate zeolite" does not include aluminophosphate materials such as SAPO, ALPO, and MeAPO materials, while the broad term "zeolite" is intended to include aluminosilicates and aluminophosphates. Zeolites are crystalline materials having a fairly uniform pore size, ranging from about 3 to 10 angstroms in diameter depending on the type of zeolite and the type and amount of cations contained in the zeolite lattice. Zeolites typically comprise a silica to alumina molar ratio (SAR) of 2 or greater.

The term "aluminophosphate" refers to another specific example of a molecular sieve, which contains aluminum and phosphate atoms. Aluminophosphates are crystalline materials with fairly uniform pore sizes.

Molecular sieves (e.g., zeolites) are generally defined as having a common angle TO₄An aluminosilicate of an open three-dimensional framework structure of tetrahedral composition, wherein T is Al or Si, or optionally P. The cations that balance the charge of the anionic backbone are loosely associated with the backbone oxygen, and the remaining pore volume is filled with water molecules. The non-framework cations are typically exchangeable, and the water molecules are removable.

In one or more embodiments, the molecular sieve material independently comprises SiO₄/AlO₄Tetrahedral and connected by common oxygen atoms to form a three-dimensional network. In other embodiments, the molecular sieve material comprises SiO₄/AlO₄/PO₄A tetrahedron. The molecular sieve material of one or more embodiments may be based primarily on a zeolite composed of (SiO)₄)/AlO₄Or SiO₄/AlO₄/PO₄The geometry of the voids formed by the rigid network of tetrahedra. The entrance to the void is formed by 6, 8, 10 or 12 ring atoms, as far as the atoms forming the entrance opening are concerned. In one or more embodiments, the molecular sieve material comprises a ring size no greater than 12 (including 6, 8, 10, and 12).

In one or more embodiments, the molecular sieve material comprises an 8-membered ring small pore aluminosilicate zeolite. The term "small pore" as used herein refers to a pore opening of less than about 5 angstroms, for example about 3.8 angstroms. The phrase "8-membered ring" zeolite refers to a zeolite having 8-membered ring pore openings and two 6-membered ring secondary structural units and having a cage structure formed by the connection of the two 6-membered ring structural units by the 4-membered ring. In one or more embodiments, the molecular sieve material is a small pore molecular sieve having a maximum ring size of 8 tetrahedral atoms.

Zeolites are composed of secondary building blocks (SBUs) and composite building blocks (CBUs) and exist in many different framework structures. Secondary building blocks contain up to 16 tetrahedral atoms and are achiral. The composite building blocks need not be achiral and need not be used to construct the entire skeleton. For example, one group of zeolites has a single four-membered ring (s4r) composite structural unit in its framework structure. In the four-membered ring, "4" represents the number of positions of tetrahedral silicon and aluminum atoms, and oxygen atoms are located between tetrahedral atoms. Other composite structural elements include, for example, single six-membered ring (s6r) elements, double four-membered ring (d4r) elements, and double six-membered ring (d6r) elements. The d4r unit is formed by linking two s4r units. The d6r unit is formed by linking two s6r units. In the d6r unit, there are 12 tetrahedral atoms. Zeolite framework types having secondary structural units of d6r include AEI, AFT, AFX, CHA, EAB, EMT, ERI, FAU, GME, JSR, KFI, LEV, LTL, LTN, MOZ, MSO, MWW, OFF, SAS, SAT, SAV, SBS, SBT, SFW, SSF, SZR, TSC, and WEN.

In one or more embodiments, the molecular sieve material comprises d6r units. Thus, in one or more embodiments, the molecular sieve material has a framework type selected from the group consisting of AEI, AFT, AFX, CHA, EAB, EMT, ERI, FAU, GME, JSR, KFI, LEV, LTL, LTN, MOZ, MSO, MWW, OFF, SAS, SAT, SAV, SBS, SBT, SFW, SSF, SZR, TSC, WEN, and combinations thereof. In another specific embodiment, the molecular sieve material has a framework type selected from the group consisting of: CHA, AEI, AFX, ERI, KFI, LEV, AFT, EAB, DDR, PAU, RHO, SAV, SAT, TSC, UEI, and combinations thereof. In yet another embodiment, the molecular sieve material has a framework type selected from CHA, AEI, and AFX. In one or more very specific embodiments, the molecular sieve material has a CHA framework type.

A zeolite CHA framework type molecular sieve comprises a zeolite having the approximate formula: (Ca, Na)₂,K₂,Mg)Al₂Si₄O₁₂·6H₂Zeolite-like naturally occurring network silicate minerals of O (e.g. hydrated calcium aluminum silicate). Breck was 1973 by John Wiley&Three synthetic forms of Zeolite CHA-framework type Molecular Sieves are described in "Zeolite Molecular Sieves" published by Sons, which is incorporated herein by reference. The three synthetic forms reported by Breck are: zeolite K-G, described in J.chem.Soc., page 2822 (1956), Barrer et al; zeolite D, described in British patent No.868,846 (1961); and Zeolite R, described in U.S. Pat. No.3,030,181, which is incorporated herein by reference. The synthesis of another synthetic form of zeolite CHA framework type SSZ-13 is described in U.S. patent No.4,544,538, which is incorporated herein by reference. The synthesis of synthetic forms of molecular sieves having the CHA framework type silicoaluminophosphate 34(SAPO-34) is described in U.S. Pat. nos. 4,440,871 and No.7,264,789, which are incorporated herein by reference. A method for preparing another synthetic molecular sieve having a CHA framework type SAPO-44 is described in U.S. patent No.6,162,415, which is incorporated herein by reference.

In one or more embodiments, the molecular sieve material may include all aluminosilicate, borosilicate, gallosilicate, MeAPSO, and MeAPO compositions. These include, but are not limited to SSZ-13, SSZ-62, natural chabazite, zeolite K-G, Linde D, Linde R, LZ-218, LZ-235. LZ-236, ZK-14, SAPO-34, SAPO-44, SAPO-47, ZYT-6, CuSAPO-34, CuSAPO-44, and CuSAPO-47.

The silica to alumina ratio of the aluminosilicate molecular sieve component can vary over a wide range. In one or more embodiments, the molecular sieve material has a silica to alumina molar ratio (SAR) of from 2 to 300 (including 5 to 250; 5 to 200; 5 to 100; and 5 to 50). In one or more specific embodiments, the molecular sieve material has a silica to alumina molar ratio (SAR) of 2 to 200 (including 10 to 200, 10 to 100, 10 to 75, 10 to 60, 10 to 50; 15 to 100, 15 to 75, 15 to 60 and 15 to 50; 20 to 100, 20 to 75, 20 to 60 and 20 to 50).

The term "promoted" as used herein refers to a component that is intentionally added to a molecular sieve material as opposed to impurities inherent in the molecular sieve. Thus, the intentional addition of the co-catalyst increases the activity of the catalyst compared to a catalyst without an intentional addition of the co-catalyst. To facilitate SCR of nitrogen oxides, in one or more embodiments, a suitable metal is independently exchanged into the molecular sieve. According to one or more embodiments, the molecular sieve is promoted with one or more of copper (Cu), iron (Fe), cobalt (Co), nickel (Ni), lanthanum (La), cerium (Ce), manganese (Mn), vanadium (V), or silver (Ag). In particular embodiments, the molecular sieve is promoted with one or more of copper (Cu) or iron (Fe). In a very specific embodiment, the molecular sieve is promoted with copper (Cu). In other embodiments, the molecular sieve is promoted with iron (Fe).

The promoter metal content of the catalyst, calculated as the oxide, is reported in one or more embodiments to be at least about 0.1 wt.% on a volatile free basis. In particular embodiments, the promoter metal content, calculated as the oxide, is from 0.1 wt.% to about 10 wt.% (including 9 wt.%, 8 wt.%, 7 wt.%, 6 wt.%, 5 wt.%, 4 wt.%, 3 wt.%, 2 wt.%, 1 wt.%, 0.5 wt.%, 0.25 wt.%, and 0.1 wt.%) based in each case on the total weight of the calcined molecular sieve reported on a volatile-free basis.

In particular embodiments, the promoter metal comprises Cu, and the Cu content, calculated as CuO, is from 0.1 wt.% to about 5 wt.% (including 5 wt.%, 4 wt.%, 3 wt.%, 2 wt.%, 1 wt.%, 0.5 wt.%, 0.25 wt.%, and 0.1 wt.%) based in each case on the total weight of the calcined molecular sieve reported on a volatile-free basis. In particular embodiments, the Cu content of the molecular sieve, calculated as CuO, is from about 2 wt.% to about 5 wt.%.

In other embodiments, the promoter metal comprises Fe, and is in the form of Fe₂O₃The calculated Fe content is in each case based on the total weight of the calcined molecular sieve reported on a volatile-free basisFrom 0.1 wt% to about 5 wt% (including 5 wt%, 4 wt%, 3 wt%, 2 wt%, 1 wt%, 0.5 wt%, 0.25 wt%, and 0.1 wt%). In particular embodiments, with Fe₂O₃The calculated Fe content of the molecular sieve is from about 2 wt% to about 5 wt%.

NH₃Oxidation catalyst

According to one or more embodiments of the present invention, effective catalytic NH is used₃The oxidation reaction composition serves as a catalyst for one or more embodiments. Reacting ammonia and oxygen contained in the exhaust stream in NH₃On oxidation catalyst to form N₂。

As further mentioned herein, NH₃The oxidation catalyst may comprise a zeolitic or non-zeolitic molecular sieve which may have any of the framework structures listed in the zeolite structure database published by the International Zeolite Association (IZA). In one or more embodiments, the molecular sieve material is a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms. In one or more specific embodiments, the molecular sieve material is selected from framework types CHA, AEI, AFX, ERI, KFI, LEV, AFT, EAB, DDR, PAU, RHO, SAV, SAT, TSC, UEI, and combinations thereof. In other embodiments, the molecular sieve material has a CHA framework type.

In one embodiment, the molecular sieve component may be physically mixed with one or more platinum group metals supported on a refractory metal oxide.

NH₃The oxidation catalyst may comprise a component active for ammonia SCR function. The SCR component may comprise any of the molecular sieve materials described in the previous sections. In one embodiment, NH₃The oxidizing component is a physical mixture of copper or iron on one or more platinum group metals supported on a refractory metal oxide and a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms. In one or more embodiments, the mixture is a homogeneous mixture. As used herein, the term "intimately mixed" or "intimate mixture" refers to a washcoat mixture in which the molecular sieve material is supported on a refractory metal oxide supportThe one or more platinum group metals above are uniformly distributed throughout the washcoat such that the washcoat is always the same.

In one or more embodiments, NH is₃The oxidizing component is separated from the SCR component, not in separate layers, but physically mixed with the SCR component.

In an embodiment of the first aspect of the invention, the catalyst for oxidizing ammonia comprises a washcoat containing copper or iron on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms mixed with platinum and rhodium on a refractory metal oxide support.

The term "platinum group metal" or "PGM" as used herein refers to one or more chemical elements defined in the periodic table of elements, including platinum (Pt), palladium (Pd), rhodium (Rh), osmium (Os), iridium (Ir), and ruthenium (Ru), and mixtures thereof.

As used herein, "platinum group metal component," "platinum component," "rhodium component," "palladium component," "iridium component," and the like, refer to platinum group metal compounds, complexes, and the like that decompose or convert to a catalytically active form, typically a metal or metal oxide, upon calcination or use of the catalyst.

In one or more embodiments of the first aspect of the present invention, the platinum group metals include platinum and rhodium. Generally, there is no particular limitation in terms of the platinum content and rhodium content of the catalyst. In one or more embodiments, the platinum loading ranges from 0.3 to 20g/ft³Including 2-20g/ft³、2-10g/ft³And 2-5g/ft³Rhodium loading of 0.3-20g/ft³Including 2-20g/ft³、2-10g/ft³And 2-5g/ft³. In one or more embodiments, the amount of platinum present in the catalyst is greater than or equal to the amount of rhodium present in the catalyst. In one or more embodiments, the ratio of Pt to Rh is equal to or greater than 1, including greater than about 1.5, greater than about 2, greater than about 5, greater than about 10, and greater than about 20.

In one or more embodiments, the catalyst of the first aspect of the invention is substantially free of other platinum group metals. As used herein, the terms "substantially free of other platinum group metals" or "free of other platinum group metals" means that no platinum group metals other than platinum and rhodium are intentionally added to the catalyst and that typically less than about 1 wt.% (including less than about 0.75 wt.%, less than about 0.5 wt.%, less than about 0.25 wt.%, and less than about 0.1 wt.%) of other platinum group metals are present in the catalyst. In other words, the catalyst does not comprise palladium (Pd), ruthenium (Ru), osmium (Os), or iridium (Ir). In one or more embodiments, the catalyst comprises platinum and no other platinum group metal. In such embodiments, the catalyst does not contain palladium (Pd), ruthenium (Ru), osmium (Os), iridium (Ir), or rhodium (Rh). In other embodiments, the catalyst comprises platinum (Pt) and rhodium (Rh) without other platinum group metals. In such embodiments, the catalyst does not contain palladium (Pd), ruthenium (Ru), osmium (Os), or iridium (Ir). However, it will be understood by those skilled in the art that trace amounts of other platinum group metals may migrate from one washcoat component to another washcoat component during loading/coating so that trace amounts of other platinum group metals may be present in the catalyst.

According to one or more embodiments, one or more platinum group metal components are deposited on a refractory metal oxide support. In particular embodiments, in the first aspect of the invention, platinum and rhodium are deposited on a refractory metal oxide support. The terms "refractory metal oxide support" and "support" as used herein refer to the underlying high surface area material upon which additional chemical compounds or elements are supported. The carrier particles have pores greater than 20 angstroms and a broad pore distribution. As defined herein, such metal oxide supports do not include molecular sieves, particularly zeolites. In particular embodiments, high surface area refractory metal oxide supports may be used, such as alumina support materials, also known as "gamma alumina" or "activated alumina," which typically exhibit over 60 square meters per gram ("m/m)²G'), usually up to about 200m²BET surface area in g or higher. Such activated aluminas are typically mixtures of gamma and delta phases of alumina, but may also contain significant amounts of eta, kappa and theta alumina phases. Refractory metal oxides other than activated alumina may be used as supports for at least some of the catalytic components in a given catalyst. For example, zirconia, alpha-alumina, silica, titania and other materials are knownFor this purpose.

One or more embodiments of the present invention include a refractory metal oxide support comprising an activating compound selected from the group consisting of alumina, silica, zirconia, titania, and physical mixtures or chemical combinations thereof including atom doping combinations. One or more embodiments of the present invention include a refractory metal oxide support comprising an activating compound selected from the group consisting of: alumina, zirconia, alumina-zirconia, lanthana-alumina, lanthana-zirconia-alumina, baria-lanthana-neodymia-alumina, alumina-chromia, and combinations thereof. In one or more embodiments, the refractory metal oxide support comprises one or more of alumina, ceria, zirconia, ceria-zirconia mixed oxide, titania, or silica, and the refractory metal oxide support may be doped with Ce, La, Ba, Zr, Hf, Ta, Mn, Si, Ti, W, Mo, and Re. In one or more embodiments, a mixed phase rich in zirconia, pure zirconia, or doped zirconia is used. Although many of these materials suffer from the disadvantage of having a significantly lower BET surface area compared to activated alumina, this disadvantage is often offset by the higher durability or performance enhancement of the resulting catalyst. The term "BET surface area" as used herein has its reference to the Brunauer, Emmett, Teller method (for use by N₂Adsorption to determine surface area). Pore diameter and pore volume BET type N can also be used₂Adsorption or desorption experiments.

In one or more embodiments, the refractory metal oxide support comprises alumina doped/stabilized with one or more of Ce, La, Ba, Zr, Hf, Ta, Mn, Si, Ti, W, Mo, and Re. In one or more embodiments, the refractory metal oxide support comprises alumina doped/stabilized with one or more of zirconia, silica, and titania. In one or more embodiments, the refractory metal oxide support comprises zirconia-doped alumina.

Generally, there is no particular limitation as to the amount of dopant/stabilizer present in the refractory metal oxide support. In one or more embodiments, the dopant (one or more of zirconia, silica, and titania) can be present in an amount of about 5 to 30 wt.% (including about 10 to 25 wt.% and about 15 to 20 wt.%) based on the total weight of the refractory metal oxide support.

Without being bound by theory, it is believed that the presence of a neutral dopant (e.g., zirconia) or an acidic dopant (e.g., silica or tungsten) prevents the reaction of copper with alumina, avoiding the formation of copper aluminate, which can adversely affect catalyst performance. In one or more embodiments, the washcoat is substantially free of copper aluminate. The phrase "substantially free of copper aluminate" as used herein means that the copper aluminate present in the washcoat is typically less than 2%. In one or more embodiments, less than 1.9%, less than 1.8%, less than 1.7%, less than 1.6%, less than 1.5%, less than 1.4%, less than 1.3%, less than 1.2%, less than 1.1%, less than 1%, less than 0.9%, less than 0.8%, less than 0.7%, less than 0.6%, less than 0.5%, less than 0.4%, less than 0.3%, less than 0.2%, and less than 0.1% of the copper aluminate is present in the washcoat.

An embodiment of the first aspect of the invention in which a catalyst is coated on a substrate is shown in figure 1. Referring to fig. 1, a layered catalytic article 100 comprises a substrate 110 coated with a catalyst 120, which is a washcoat comprising a mixture of copper on a molecular sieve material 130 and platinum and rhodium on a refractory metal oxide support 140. The substrate 110 has an inlet end 150 and an outlet end 160 defining an axial length L1. In one or more embodiments, the substrate 110 generally comprises a plurality of channels 170 of a honeycomb substrate, of which only one channel is shown in cross-section for clarity. As will be understood by those skilled in the art, the length of the catalyst 120 on the substrate 110 may vary such that the catalyst 120 covers the entire substrate 110 or only a portion of the substrate 110.

Embodiments of the second aspect of the invention are directed to catalysts for oxidizing ammonia comprising a first washcoat region and a second washcoat region. In one or more embodiments, the first washcoat region comprises copper or iron on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms, wherein the first washcoat region is substantially free of platinum group metals; and the second washcoat zone comprises copper or iron on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms mixed with platinum on the refractory metal oxide support.

As noted above, in the second washcoat region, NH₃The oxidizing component may be a physical mixture of one or more platinum group metals supported on a refractory metal oxide and copper or iron on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms. In one or more embodiments, the mixture is a homogeneous mixture.

As used herein, the term "substantially free of platinum group metals" means that no platinum group metals are present in the first washcoat zone on purpose, and typically less than about 1 wt.% (including less than about 0.75 wt.%, less than about 0.5 wt.%, less than about 0.25 wt.%, less than about 0.1 wt.%) platinum group metals are present in the first washcoat zone. However, those skilled in the art will appreciate that trace amounts of platinum group metals may migrate from one washcoat zone component to another washcoat zone component during loading/coating such that trace amounts of platinum group metals may be present in the first washcoat zone.

In one or more embodiments, the first washcoat region and the second washcoat region are disposed in an axially zoned configuration. The term "axially-zoned" as used herein refers to the position of the first washcoat region and the second washcoat region relative to each other. Axial means side-by-side such that the first washcoat region and the second washcoat region are disposed one after the other. In one or more embodiments, the first washcoat zone and the second washcoat zone are disposed on a monolithic substrate. In one or more embodiments, the first washcoat region and the second washcoat region are disposed on the same or a common substrate. In other embodiments, the first washcoat region and the second washcoat region are disposed on separate substrates.

In one or more embodiments, the first washcoat zone is located upstream of the second washcoat zone. The terms "upstream" and "downstream" as used herein refer to the relative direction of flow of the engine exhaust stream from the engine to the tailpipe, with the engine at an upstream location and the tailpipe and any pollution abatement articles such as filters and catalysts downstream of the engine.

In one or more embodiments, the second washcoat region comprises platinum and no other platinum group metals. Generally, there is no particular limitation as to the platinum content of the second washcoat region. In one or more embodiments, the platinum loading ranges from 0.3 to 20g/ft³Including 2-20g/ft³、2-10g/ft³And 2-5g/ft³. In other embodiments, the second washcoat region comprises platinum and further comprises rhodium in the absence of other platinum group metals. Generally, there is no particular limitation with respect to the platinum content and rhodium content of the second washcoat region. In one or more embodiments, the platinum loading ranges from 0.3 to 20g/ft³Including 2-20g/ft³、2-10g/ft³And 2-5g/ft³And the rhodium loading is 0.3-20g/ft³Including 2-10g/ft³、2-10g/ft³And 2-5g/ft³. In one or more embodiments, the amount of platinum present in the catalyst is greater than or equal to the amount of rhodium present in the catalyst. In one or more embodiments, the ratio of Pt to Rh is equal to or greater than 1, including greater than about 1.5, greater than about 2, greater than about 5, greater than about 10, and greater than about 20.

In one or more embodiments, the molecular sieve material of the first washcoat region and/or the second washcoat region is a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms. In one or more specific embodiments, the molecular sieve material of the first washcoat zone and/or the second washcoat zone is selected from framework types CHA, AEI, AFX, ERI, KFI, LEV, AFT, EAB, DDR, PAU, RHO, SAV, SAT, TSC, UEI, and combinations thereof. In other embodiments, the molecular sieve material of the first washcoat region and/or the second washcoat region has a CHA framework type.

In one or more embodiments, the refractory metal oxide support of the second washcoat zone can include any of the refractory metal oxide supports described above. In one or more specific embodiments, the refractory metal oxide support of the second washcoat region comprises alumina, silica, zirconia, titania, and physical mixtures thereof or chemical combinations including atomic doping combinations.

Embodiments of the second aspect of the invention in which a catalyst is coated on a substrate are shown in fig. 2A and 2B. Referring to FIG. 2A, an exemplary embodiment of an axially zoned catalytic article is shown. An axially zoned catalytic article 200 is shown in which a first washcoat zone 220 is located upstream of a second washcoat zone 230 on a substrate 210. The first washcoat zone 220 contains copper or iron on molecular sieves. The second washcoat zone 230 comprises a mixture of copper or iron on a molecular sieve material 240 and platinum and rhodium on a refractory metal oxide support 250. The substrate 210 has an inlet end 260 and an outlet end 270 defining an axial length L2. In one or more embodiments, the substrate 210 generally comprises a plurality of channels 280 of a honeycomb substrate, of which only one channel is shown in cross-section for clarity. The first washcoat zone 220 extends from the inlet end 260 of the substrate 210 through less than the entire axial length L2 of the substrate 210. The length of first washcoat region 220 is represented in fig. 2 as first washcoat region length 2230 a. The second washcoat zone 230 extends from the outlet end 270 of the substrate 210 through less than the entire axial length L2 of the substrate L2. The length of the second washcoat region 230 is represented in fig. 2A and 2B as a second washcoat region length 230 a.

In one or more embodiments, as shown in fig. 2A, a first washcoat zone 220 comprising copper or iron on molecular sieves is directly adjacent to a second washcoat zone 230 comprising a mixture of copper or iron on molecular sieve material 240 and platinum and rhodium on a refractory metal oxide support 250. In other embodiments, as shown in fig. 2B, a first washcoat zone 220 comprising copper or iron on molecular sieves and a second washcoat zone 230 comprising a mixture of copper or iron on molecular sieve material 240 and platinum and rhodium on refractory metal oxide support 250 can be separated by a gap 290.

Referring to fig. 2A and 2B, it will be appreciated that the lengths of the first washcoat region 220 and the second washcoat region 230 can vary. In one or more embodiments, the first washcoat region 220 and the second washcoat region 230 can be equal in length. In other embodiments, the first washcoat region 220 can be about 10-90% or about 20-80% of the length L2 of the substrate 210 with the second washcoat region 230 covering the remainder of the length L2 of the substrate 210, respectively, as shown in fig. 2A. In other embodiments, as shown in fig. 2B, with the voids 290, the first washcoat region 220 may be about 10%, about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, or about 90% of the length L2 of the substrate 210, with the second washcoat region 230 covering the remainder of the length L2 of the substrate 210, respectively.

Those skilled in the art will also appreciate that the first washcoat region and the second washcoat region may at least partially overlap (not shown). The term "at least partially overlap" as used herein means that the first washcoat region and the second washcoat region can overlap each other in an amount of at least about 0.1% to at least about 99%. In one or more embodiments, the first washcoat region and the second washcoat region can completely overlap. In one or more embodiments, the first washcoat region partially overlaps the second washcoat region. In other embodiments, the second washcoat region partially overlaps the first washcoat region.

Base material

In one or more embodiments, the catalyst material may be applied to the substrate as a washcoat. The term "substrate" as used herein refers to a monolithic material on which a catalyst (typically in the form of a washcoat) is disposed. The washcoat is formed by preparing a slurry comprising the catalyst at a specified solids content (e.g., 30-90 wt%) in a liquid medium, which is then applied to a substrate and dried to provide the washcoat.

In one or more embodiments, the substrate is a ceramic or metal having a honeycomb structure. Any suitable substrate may be used, for example a monolithic substrate of the type having fine parallel gas flow channels extending therethrough from an inlet or outlet face of the substrate, such that the channels are open to fluid flowing therethrough. The channels, which are substantially straight paths from their fluid inlets to their fluid outlets, are defined by walls on which the catalytic material is coated as a washcoat, such that gases flowing through the channels contact the catalytic material. The flow channels of the monolithic substrate are thin-walled channels, which may have any suitable cross-sectional shape and size, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, oval, circular, and the like. Such structures may contain from about 60 to about 900 or more gas inlet openings (i.e., apertures) per square inch of cross-section.

The ceramic substrate may be made of any suitable refractory material, such as cordierite, cordierite-alpha-alumina, silicon nitride, zircon mullite (zirconia mullite), spodumene, alumina-silica-magnesia, zirconium silicate, sillimanite, magnesium silicate, zircon, petalite, alpha-alumina, aluminosilicates, and the like.

The substrates useful for the catalysts of embodiments of the present invention may also be metallic in nature and may be composed of one or more metals or metal alloys. The metal substrate may be used in various shapes, such as pellets, corrugated sheets, or monoliths. Specific examples of metal substrates include heat-resistant base metal alloys, especially those in which iron is the substantial or major component. Such alloys may include one or more of nickel, chromium, and aluminum, and the total amount of these metals may advantageously comprise at least about 15 wt.% of the alloy, such as about 10-25 wt.% chromium, about 1-8 wt.% aluminum, and about 0-20 wt.% nickel.

In one or more embodiments, the catalyst for oxidizing ammonia may be coated on a high porosity ceramic honeycomb flow through support. The high porosity ceramic honeycomb flow-through support may have the following properties: a majority of the interconnected pores; a porosity of the wall material greater than about 50% and up to about 70%; an average pore size greater than 20 microns, such as greater than 25 microns, more specifically greater than about 30 microns, more specifically greater than about 40 microns but less than about 100 microns; and a broad pore size distribution.

In one or more embodiments, the catalyst for oxidizing ammonia of one or more embodiments may be coated on a wall-flow filter. As recognized by those skilled in the art, when the selective catalytic reduction article is coated on a wall-flow filter, the result is SCR on the filter. In one or more embodiments, a catalyst comprising a washcoat containing copper or iron on a molecular sieve material mixed with platinum and rhodium on a refractory metal oxide support may be coated on a wall-flow filter.

In other embodiments, a first washcoat zone comprising copper or iron on a molecular sieve material is coated on a wall-flow filter such that an SCR on the filter is produced, and a second washcoat zone comprising copper or iron on a molecular sieve material mixed with platinum on a refractory metal oxide support is coated on a flow-through monolith. In yet another embodiment, both the first washcoat zone and the second washcoat zone are coated on a wall-flow filter. In such embodiments where both the first washcoat zone and the second washcoat zone are coated on a wall-flow filter, the first washcoat zone and the second washcoat zone may be coated on a single wall-flow filter, or the first washcoat zone and the second washcoat zone may be coated on separate wall-flow filters such that two bricks are present in the exhaust gas treatment system.

Fig. 3A and 3B show a wall-flow filter substrate 300 having a plurality of channels 352. The channels are closed in a tubular manner by the channel walls 353 of the filter substrate. The substrate has an inlet end 354 and an outlet end 356. The alternate channels are plugged at the inlet end with an inlet plug 358 and at the outlet end with an outlet plug 360 to form an opposing checkerboard pattern at the inlet end 354 and the outlet end 356. Gas stream 362 enters through unplugged channel inlet 364, is stopped by outlet plug 360, and diffuses through channel walls 353 (which are porous) to outlet side 366. Due to the inlet plug 358, the gas cannot return to the inlet side of the wall.

In one or more embodiments, the wall-flow filter substrate is composed of a ceramic-like material such as cordierite, alpha-alumina, silicon carbide, silicon nitride, zirconia, mullite, spodumene, alumina-silica-magnesia, or zirconium silicate, or a porous refractory metal. In other embodiments, the wall flow substrate is formed from a ceramic fiber composite. In particular embodiments, the wall flow substrate is formed from cordierite and silicon carbide. Such materials are capable of withstanding the environments, particularly high temperatures, encountered when treating effluent streams.

In one or more embodiments, the wall-flow substrate comprises a porous thin-walled honeycomb monolith through which the fluid stream is passed without causing excessive back pressure or pressure increase on the article. Typically, the presence of a clean wall flow article will produce a back pressure of 1 inch of water to 10 psig. The ceramic wall flow substrate used in the system is formed of a material having a porosity of at least 50% (e.g., 50-75%) and an average pore size of at least 5 microns (e.g., 5-30 microns). In one or more embodiments, the substrate has a porosity of at least 55% and has an average pore size of at least 10 microns. When substrates having these porosities and these average pore sizes are coated by the techniques described below, a sufficient amount of the catalyst composition can be supported on the substrate to achieve excellent NO_xThe conversion efficiency. These substrates are capable of maintaining adequate exhaust flow characteristics, i.e., acceptable backpressure, despite SCR catalyst loading. The disclosure of U.S. patent No.4,329,16 for suitable wall flow substrates is incorporated herein by reference.

Typical wall-flow filters for commercial use have a lower wall porosity, e.g., about 35-50%, than the wall-flow filters used in the present invention. Typically, commercial wall flow filters have very broad pore size distributions with average pore sizes less than 17 microns.

The porous wall flow filter used in one or more embodiments is catalyzed in that the walls of the member have thereon or comprise therein one or more catalytic materials. The catalytic material may be present only on the inlet side, only on the outlet side, on the inlet side and on the outlet side of the walls of the member, or the walls themselves may be composed wholly or partly of catalytic material. The invention includes the use of a combination of one or more layers of catalytic material and one or more layers of catalytic material on the inlet and/or outlet walls of the member.

To coat a wall-flow substrate with the catalytic article of one or more embodiments, the substrate is immersed vertically into a portion of the catalyst slurry such that the top of the substrate is located just above the surface of the slurry. In this manner, the slurry contacts the inlet face of each honeycomb wall, but is prevented from contacting the outlet face of each wall. The sample remained in the slurry for about 30 seconds. The substrate is removed from the slurry and excess slurry is removed from the wall flow substrate by first allowing it to drain from the channels, then by blowing with compressed air (opposite the direction of slurry penetration), and then by drawing a vacuum from the direction of slurry penetration. By using this technique, the catalyst slurry penetrates the walls of the substrate, but the pores do not clog to the extent that an undue back pressure is created in the finished substrate. As used herein, the term "permeate," when used to describe the dispersion of the catalyst slurry on the substrate, means that the catalyst composition is dispersed throughout the walls of the substrate.

The coated substrate is typically dried at about 100 ℃ and calcined at higher temperatures (e.g., 300 ℃ C. and 450 ℃ C.). After calcination, the catalyst loading can be determined by calculating the weight of the coated and uncoated substrates. As will be understood by those skilled in the art, the catalyst loading can be varied by varying the solids content of the coating slurry. Alternatively, repeated dipping of the substrate in the coating slurry may be performed, followed by removal of excess slurry as described above.

Carrier coating

According to one or more embodiments, NH₃The oxidation catalyst may be applied in a washcoat layer, which is applied to the washcoat and adhered to the substrate. The term "washcoat" as used herein has its usual meaning in the art of thin adherent coatings of catalytic or other materials applied to a substrate material (e.g., a honeycomb support assembly) that is sufficiently porous to allow passage of a stream of the treated gas.

For example, containing NH₃The washcoat of the oxidation catalyst composition may be formed by preparing a mixture or solution of copper or iron on the molecular sieve material with a platinum precursor and/or a rhodium precursor in a suitable solvent such as water. In general, aqueous solutions of soluble compounds or complexes of platinum and/or rhodium are preferred from an economic and environmental point of viewAnd (4) selecting. Typically, the platinum and/or rhodium precursor is used in the form of a compound or complex to achieve dispersion of the platinum precursor and/or rhodium precursor on the support. For the purposes of the present invention, the terms "platinum precursor", "rhodium precursor", "palladium precursor" and the like are intended to mean any compound, complex or the like which decomposes or converts to a catalytically active form in the initial stage of calcination or use thereof. Suitable platinum complexes or compounds include, but are not limited to, platinum chlorides (e.g., [ PtCl ]₄]^2-，[PtCl₆]^2-Salts), platinum hydroxides (e.g. [ Pt (OH)₆]^2-Salts), platinum ammine (e.g. [ Pt (NH) ]₃)₄]²⁺、Pt(NH₃)₄]⁴⁺Salts), platinum hydrates (e.g., [ Pt (OH)₂)₄]²⁺Salts), bis (acetylacetonato) platinum and mixed compounds or complexes (e.g. [ Pt (NH) ]₃)₂(Cl)₂]). However, it is to be understood that the present invention is not limited to a particular type, composition, or purity of platinum precursor.

Suitable rhodium complexes or compounds include, but are not limited to, rhodium chloride, rhodium hydroxide, rhodium nitrate, and the like. In one or more embodiments, a rhodium nitrate solution is used, which may be prepared by reacting Rh with Rh₂O₃Prepared by dissolution in nitrous acid (nitroeous acid) and can be expressed as dissolved Rh (NO)₃)₃。

However, it is to be understood that the present invention is not limited to rhodium precursors of a particular type, composition or purity. The mixture or solution of platinum and/or rhodium precursors is added to the support by one of several chemical methods. These include impregnation of the platinum precursor and/or rhodium precursor solution onto the support, followed by a fixation step that can incorporate an acidic component (e.g., acetic acid) or a basic component (e.g., ammonium hydroxide). The wet solid may be chemically reduced or calcined or used as such. Alternatively, the support may be suspended in a suitable medium (e.g., water) and reacted with the platinum precursor and/or the rhodium precursor in solution. Additional processing steps may include fixation, chemical reduction or calcination by acidic components (e.g., acetic acid) or basic components (e.g., ammonium hydroxide).

In the use of SCR composition carrier coatingIn one or more embodiments, the layer may comprise a zeolitic molecular sieve or a non-zeolitic molecular sieve having distributed thereon a metal selected from one or more of copper (Cu), iron (Fe), cobalt (Co), nickel (Ni), lanthanum (La), cerium (Ce), manganese (Mn), vanadium (V), or silver (Ag). An exemplary metal of this family is copper. Exemplary molecular sieves include, but are not limited to, zeolites having the following crystal structures: CHA, AEI, AFX, ERI, KFI, LEV, AFT, EAB, DDR, PAU, RHO, SAV, SAT, TSC, UEI, and combinations thereof. A suitable method for distributing the metal on the zeolite is to first prepare a mixture or solution of the metal precursors in a suitable solvent such as water. Generally, an aqueous solution of a soluble metal compound or metal complex is preferable from the economical and environmental aspects. For the purposes of the present invention, the term "metal precursor" means any compound, complex, etc., which can be dispersed on a zeolite support to produce a catalytically active metal component. For copper, suitable complexes or compounds include, but are not limited to, anhydrous and hydrated copper sulfate, copper nitrate, copper acetate, copper acetylacetonate, copper oxide, copper hydroxide, and copper amine salts (e.g., [ Cu (NH)₃)₄]²⁺). However, it is to be understood that the present invention is not limited to a particular type, composition, or purity of metal precursor. The molecular sieve may be added to a solution of the metal component to form a suspension. The suspension may be reacted such that the copper component is distributed on the zeolite. This may result in copper being distributed in the channels and on the outer surface of the molecular sieve. The copper may be distributed as copper (II) ions, copper (I) ions or as copper oxide. After the copper has been distributed over the molecular sieve, the solid can be separated from the liquid phase of the suspension, washed and dried. The resulting copper-containing molecular sieve can also be calcined to fix the copper.

For applying a washcoat according to one or more embodiments of the present invention, an SCR component, NH, will be included₃The finely divided particles of catalyst of the oxidation catalyst or mixtures thereof are suspended in a suitable medium such as water to form a slurry. Other promoters and/or stabilizers and/or surfactants may be added to the slurry as a mixture or solution in water or water-miscible medium. In one or more embodiments, the slurry is comminuted/ground to result in substantially all solids having an average diameter of less than aboutA particle size of 10 microns, i.e., about 0.1-8 microns. The comminution/grinding may be carried out in a ball mill, continuous Eiger mill or other similar equipment. In one or more embodiments, the suspension or slurry has a pH of about 2 to less than about 7. The pH of the slurry can be adjusted by adding an appropriate amount of inorganic or organic acid to the slurry, if necessary. The solids content of the slurry may be, for example, from about 20 to 60 weight percent, more particularly from about 35 to 45 weight percent. The substrate can then be immersed in the slurry or the slurry can be coated onto the substrate such that a desired loading of the catalyst layer is deposited on the substrate. Thereafter, the coated substrate is dried at about 100 ℃ and calcined by heating, for example at 300-650 ℃ for about 1 hour to about 3 hours. Drying and calcination are generally carried out in air. If desired, the coating, drying and calcining processes may be repeated to achieve the final desired weight amount of catalyst washcoat on the support. In some cases, complete removal of liquids and other volatile components may not be possible until the catalyst is placed into service and subjected to the high temperatures encountered during operation.

After calcination, the catalyst washcoat loading can be determined by calculating the difference in weight of the coated and uncoated substrates. As understood by those skilled in the art, the catalyst loading can be varied by varying the solids content of the coating slurry and the slurry viscosity. Alternatively, repeated dipping of the substrate in the coating slurry may be performed, followed by removal of excess slurry as described above.

Method for treating emissions

Another aspect of the invention includes a method of treating emissions produced in an exhaust stream of a lean burn engine. The exhaust stream may include NO_xOne or more of CO, hydrocarbons and ammonia. In one or more embodiments, the method includes injecting ammonia or an ammonia precursor into the exhaust stream, and then passing the exhaust stream over the catalyst of one or more embodiments.

Emissions treatment system

Another aspect of the invention relates to an emissions treatment system that includes one or more additional components for treating diesel exhaust emissions. Diesel engineEngine exhaust is a heterogeneous mixture of gases that contains not only gaseous emissions (e.g., carbon monoxide, unburned hydrocarbons, and NO)_x) Also included are condensed phase materials (liquids and solids) that constitute the particulate or granular material. Typically, the catalyst composition and substrate with the composition disposed thereon are provided in a diesel engine exhaust system to convert some or all of these exhaust components to innocuous components. For example, diesel exhaust systems are used in addition to reducing NO_xMay further comprise one or more of a diesel oxidation catalyst and a soot filter. Embodiments of the present invention may be incorporated into a diesel exhaust treatment system. One such system is disclosed in U.S. Pat. No.7,229,597, the entire contents of which are incorporated herein by reference.

An example of an emissions treatment system may be more readily understood with reference to fig. 4, which depicts a schematic diagram of an emissions treatment system 400 in accordance with one or more embodiments of the present invention. Containing gaseous pollutants (e.g. unburned hydrocarbons, carbon monoxide and NO)_x) And particulate matter, from the engine 410 via line 415 to a Diesel Oxidation Catalyst (DOC) 420. In a DOC, unburned gases and non-volatile hydrocarbons, as well as carbon monoxide, are largely substantially combusted to form carbon dioxide and water. In addition, NO_xA portion of the NO of the component may be oxidized to NO in the DOC₂. The effluent stream is then sent via line 425 to a Catalyzed Soot Filter (CSF)430, which captures particulate matter present within the exhaust stream. CSF is optionally catalyzed for passive regeneration. After particulate matter is removed via CSF 430, the exhaust stream is sent via line 435 to downstream catalyst 440. The downstream catalyst 440 may be a catalyst according to one or more embodiments described herein for treating and/or converting nitrogen oxides and ammonia.

In other embodiments, the downstream catalyst 440 may be an SCR catalyst. In embodiments where the downstream catalyst 440 is an SCR catalyst, the exhaust treatment system includes one or more urea storage tanks, urea pumps, urea metering systems, urea injectors/nozzles, and respective control units 455 (for injecting a source of ammonia into the exhaust stream) upstream of the SCR catalyst 440. In such embodiments, the exhaust treatment system can further include an ammonia oxidation catalyst 450 downstream of the SCR catalyst 440 via line 445. The ammonia oxidation catalyst 450 may be a catalyst according to one or more embodiments described herein.

The invention will now be described with reference to the following examples. Before describing several exemplary embodiments of the invention, it is to be understood that the invention is not limited to the details of construction or process steps set forth in the following description. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

Examples

Preparation of the catalyst

Example 1: no PGM

A solution of zirconium oxide acetate (zirconia acetate) (1.3kg) was mixed with deionized water (9kg) in a vessel. Cu-SSZ-13(8.6kg) with 3 wt% CuO was added to the mixture to form a dispersion, and the resulting dispersion was milled with a ball mill until the particle size measurement gave a particle size distribution with 90% of the particles being less than 5 microns.

In a separate vessel, 20 wt.% zirconia doped alumina powder (716g) was added to deionized water (4.5kg) containing tartaric acid (13mg) and monoethanolamine (5 mg). The pH of the mixture was adjusted to 4 with tartaric acid. Thereafter, the mixture was milled with a ball mill to obtain a particle size distribution in which 90% of the particles were less than 10 μm.

Example 2: pt only

The zirconia acetate solution (1.3kg) was mixed with deionized water (9kg) in a vessel. To this solution was added Cu-SSZ-13(8.6kg) with 3 wt% CuO and the resulting dispersion was ball milled until the particle size measurement gave a particle size distribution with 90% of the particles being less than 5 microns.

In a separate vessel, a platinum monoethanol solution (45g) with 17 wt% Pt was mixed with deionized water (100 ml). The mixture was added dropwise to 20 wt% zirconia-doped alumina powder (716 g). The resulting powder was then calcined in air at 600 ℃ for 2 hours in a box furnace. The calcined powder was added to deionized water (4.5kg) containing tartaric acid (13mg) and monoethanolamine (5 mg). The pH of the mixture was adjusted to 4 with tartaric acid. Thereafter, the mixture was milled with a ball mill to obtain a particle size distribution in which 90% of the particles were less than 10 μm.

The resulting slurry was coated on a ceramic honeycomb substrate to obtain 3.25g/in after calcination at 600 ℃ for 2 hours³The amount of the supported catalyst. Amox with Pt, Pt/Rh on Zr-doped alumina 3.25g/in³Amount of (2) to be charged]

Example 3: partitioning

Zoned catalysts were prepared from the slurries from examples 1 and 2 in the following manner:

the slurry from example 1 was coated on the 50% of the inlet section of the honeycomb and the platinum-containing slurry of example 2 was coated on the remaining 50% of the rear region of the honeycomb. In this manner, platinum was located only 50% of the rear of the honeycomb.

Example 4: Pt/Rh

The zirconia acetate solution (1.3kg) was mixed with deionized water (9kg) in a vessel. To this mixture was added Cu-SSZ-13(8.6kg) with 3 wt% CuO and the resulting dispersion was ball milled until the particle size measurement gave a particle size distribution with 90% of the particles being less than 5 microns.

In another vessel, a platinum monoethanol solution (10g) with 17 wt% Pt was mixed with deionized water (100 ml). The mixture was added dropwise to 20 wt% zirconia-doped alumina powder (716 g). A rhodium nitrate solution (33ml) having 10 wt% Rh was then added dropwise to the platinum alumina powder. The resulting powder was then calcined in air at 600 ℃ for 2 hours in a box furnace. The calcined powder was added to deionized water (4.5kg) containing tartaric acid (13mg) and monoethanolamine (5 mg). The pH of the mixture was adjusted to 4 with tartaric acid. Thereafter, the mixture was milled with a ball mill to obtain a particle size distribution in which 90% of the particles were less than 10 μm.

Example 5: rh

In another vessel, a rhodium nitrate solution (85g) with 9 wt% Rh was mixed with deionized water (100 ml). The mixture was added dropwise to 20 wt% zirconia-doped alumina powder (716 g). The resulting powder was then calcined in air at 600 ℃ for 2 hours in a box furnace. The calcined powder was added to deionized water (4.5kg) containing tartaric acid (13mg) and monoethanolamine (5 mg). The pH of the mixture was adjusted to 4 with tartaric acid. Thereafter, the mixture was milled with a ball mill to obtain a particle size distribution in which 90% of the particles were less than 10 μm.

The resulting slurry was coated on a ceramic honeycomb substrate to obtain 3.25g/in after calcination at 600 ℃ for 2 hours³The amount of the supported catalyst.

Example 6: Pt/Pd

In another vessel, a platinum monoethanolamine solution with 17 wt.% Pt (26g) was mixed with deionized water (100 ml). The mixture was added dropwise to 20 wt% zirconia-doped alumina powder (716 g). A palladium nitrate solution (15ml) having 20 wt% Pd was then added dropwise onto the platinum alumina powder. The resulting powder was then calcined in air at 600 ℃ for 2 hours in a box furnace. The calcined powder was added to deionized water (4.5kg) containing tartaric acid (13mg) and monoethanolamine (5 mg). The pH of the mixture was adjusted to 4 with tartaric acid. Thereafter, the mixture was milled with a ball mill to obtain a particle size distribution in which 90% of the particles were less than 10 μm.

Example 7

First slurry: a platinum monoethanol solution (330g) with 17 wt% Pt was mixed with deionized water (100 ml). The mixture was added dropwise to 1.5 wt% silica-doped alumina powder (716 g). To the powder were added water (800ml) and glacial acetic acid (450 g). Subsequently, the powder was placed in deionized water (4.5kg) and ball milled at pH4 to obtain a particle size distribution with 90% of the particles being less than 7.5 microns.

The resulting slurry was coated onto a ceramic honeycomb substrate to obtain 40% coverage of the rear region of the honeycomb. The loading of the coating after calcination at 600 ℃ for 2 hours was 0.2g/in³。

And (3) second slurry: the zirconia acetate solution (1.3kg) was mixed with deionized water (9kg) in a vessel. To this mixture was added Cu-SSZ-13(8.6kg) with 3 wt% CuO and the resulting dispersion was ball milled until the particle size measurement gave a particle size distribution with 90% of the particles being less than 5 microns.

The resulting slurry was coated on a ceramic honeycomb substrate to obtain 2.85g/in after calcination at 600 ℃ for 2 hours³The amount of the supported catalyst.

Example 8: no PGM

The zirconia acetate solution (1.3kg) was mixed with deionized water (9kg) in a vessel. To this mixture was added Cu-SSZ-13(8.6kg) with 3 wt% CuO to form a dispersion, and the resulting dispersion was milled with a ball mill until the particle size measurement gave a particle size distribution with 90% of the particles being less than 5 microns.

The resulting slurry was coated on a ceramic honeycomb substrate to obtain 3g/in after calcination at 600 ℃ for 2 hours³The amount of the supported catalyst.

Table 1 summarizes the catalyst formulations.

TABLE 1

Example 9: testing

Under hydrothermal conditions (10% H)₂O and 10％O₂And 80% N₂) After 16 hours of aging, SCR activity was tested under steady state engine operating conditions. For this test, the engine was adjusted to provide 250-300ppm NO_xThe discharge amount reaches the required exhaust temperature. If a constant temperature is reached, urea is injected after the DOC/filter tank is filled. The amount of urea was adjusted to reach 1.2 NH₃With NO_xAnd 20ppm NH measured after the catalyst₃Followed by 10 minutes. After stopping urea dosing, the measurement is extended until NO_xThe conversion is reduced to less than 5%.

Table 2 shows the catalyst set-up for the stationary engine bench evaluation.

TABLE 2

Table 3 shows the engine operating points and exhaust conditions for the stationary gantry evaluations.

TABLE 3

Example 10: results

Table 4 shows the remaining results of the stationary engine rig evaluation.

TABLE 4

All samples had comparable NO at 220 deg.C_xAnd (4) conversion rate. However, for the Pt-containing samples (examples 3, 4 and 7), NO at 370 ℃ and 650 ℃_xThe conversion rate is low. Example 5 containing only Rh had the same NO as example 1_xConversion rate, therefore Rh vs. selective NO_xThe reduction appears inert. The Pt-only sample (example 3) has the lowest NO at higher temperatures_xConversion and higher N₂O is formed. Negative NO at 650 DEG C_xConversion means NH₃High rate conversion of feed to unwanted NO_x. Low NH at full load obtained for Pt/Rh sample (example 4)₃Emissions indicate that the technology is at low N₂O has a high NH content when formed₃The rate of oxidation.

However, the sample containing Pt and Rh at 370 ℃ (example 4) had a lower N than the partitioned example 7 sample₂O formation and the same NO_xAnd (4) conversion rate. The results show that adding Rh to Pt reduces N₂O formation and maintenance of high NH₃The rate of oxidation.

Example 11: testing

The Artemis test was performed with a 2L EU6 engine, where the system consists of a DOC, SCR on filter in close connection with the engine and AMOx-SCR catalyst located 1.5 meters downstream of the engine. All AMOx catalysts were hydrothermally aged in an oven at 750 ℃ (10% H) prior to measurement₂O and 10% O₂And 80% N₂) For 16 hours.

Table 6 shows the catalyst set-up for the Artemis test on the engine bench.

TABLE 6

NH to 1.06 at DOC₃With NO_xAfter this ratio, urea is metered into the discharge system.

Table 7 shows the emission results using different AMOx catalysts in the system.

TABLE 7

Using PGM-freeExample 1 the most preferred emissions results were obtained. However, in this case, ammonia emissions are difficult to avoid. All Pt-containing samples were completely free of NH₃Emission, lowest N in these samples₂O and minimum NO_xThe sample discharged was a Pt/Rh-containing sample (example 4). Example 7 results in a higher N₂And (4) discharging the O.

To further evaluate the potential of the Pt/Rh samples (example 4), a laboratory test was conducted which simulates the dynamic Artemis test protocol, wherein the conditions in the exhaust manifold after a soot filter with Cu-zeolite coating (SCR on filter) in the bottom position of a 2L VW EU6 engine were simulated with NO feed only. In this test, ammonia was metered dynamically to obtain an NH of 1.2₃With NO_xThe ratio of.

Table 8: laboratory reactor Artemis test, feed gas: NO only

The results in Table 8 show that all PGM-containing samples completely removed NH₃But with total NO_xThe rate translates into a cost. Most preferred NO is achieved without PGM_xConversion (example 1). However, NH free was obtained using the Pt/Rh sample (example 4)₃Lowest N at discharge₂And (4) discharging the O.

Selective catalytic reduction of NO with ammonia by mixing Pt/Rh supported on gamma-alumina doped material with Cu-CHA zeolite_xTo prepare a very effective ammoxidation catalyst. The mixing is carried out in such a way that the Pt/Rh/doped alumina is spatially separated from the zeolitic material.

In addition, Pt and Rh do not migrate to the zeolite particles and remain located on the doped alumina particles. The Cu migrates to the doped alumina particles in such a way that the Cu concentration found on the doped alumina particles is the same or slightly higher than that found on the zeolite particles. Rh alloyed with Pt, thus strongly reduced NO₂And N₂The reaction rate of O formation. With example 7 (according to WO 2)010/012730), this design allows for higher Pt concentrations to be applied and therefore higher ammonia oxidation rates to be achieved.

Without being bound by theory, it is believed that the homogeneous design (example 4) has advantages over the layered design of example 7 in that the nitroxide formed on Pt can react with the ammonia absorbed in the immediate vicinity of the doped alumina particles to form the desired N₂. In this way, even at very high ammonia or urea dosing rates, it is possible to achieve N₂High selectivity of formation.

Example 12: testing

And (3) testing conditions are as follows:

maximum NO_xEngine outlet concentration 1500ppm, mean NO_xThe concentration was 145 ppm. Maximum AMOx inlet (SCR at filter outlet) concentration 1100ppm, mean NO_xThe concentration was 50 ppm. The maximum AMOx space velocity is 150,000h^-1The average airspeed is 32000h^-1. The maximum AMOx inlet temperature was 420 ℃ and the average temperature was 192 ℃.

Table 9 below shows NO in g/Km before DOC and after SCR on DOC plus filter system_xAnd (4) discharging the amount. In addition, reduced NO on the underlying AMOx catalyst_xAnd N downstream of AMOx catalyst₂O and NH₃The emissions are given in g/Km. NO removal by AMOx_xThe highest value of the amount indicates the most preferred result.

TABLE 9

The example 1 catalyst without PGM provides the most preferred NO_xReduced and lowest N₂O rowRelease, but not remove, the unwanted NH₃And (5) discharging. The prior art AMOx catalyst with Pt bottom coating on silica doped alumina in the rear region (example 2) effectively removed ammonia emissions, but also resulted in NO removal_xAnd results in a high N₂O emissions due to NH₃By oxidation to NO_xAnd N₂O instead of N₂。

The results were compared to 5g/ft according to the invention³AMOx catalyst homogeneously mixed into Cu-CHA coating (example 2). In this case, NO on AMOx catalyst_xThe removal rate is again negative, but N₂The O emission is low. The situation improved if this Pt-containing catalyst was coated only on 50% of the rear zone (example 3).

Further, Pt in the uniform AMOx design can be alloyed with Pd or Rh. Example 5 shows the results with Pd and example 6 shows the results with Rh. Catalyst with Rh (example 4) achieved lower N₂O and NH₃The amount of emission, therefore, the use of Rh is beneficial. In particular, if NO is added_xAnd N₂The advantage of using Rh in comparison with examples 2, 6 and 4 becomes evident because of the high NO content of Rh-containing catalysts_xMinimum NH conversion efficiency₃And N₂And (4) discharging the O.

Example 13: testing

Additional evaluations of the different examples were performed in a laboratory reactor with samples of 1 inch diameter and 4 inches length.

Test conditions, laboratory tests: the exhaust conditions simulated the Artemis test protocol for the EU6 engine with a temperature under the floor (initial temperature 20 ℃, maximum temperature 360 ℃, average temperature 220 ℃). The maximum space velocity is 180,000h^-1Average space velocity of 54,000h^-1. Maximum NO_xEmission 580ppm, average NO_xThe test discharge was 80 ppm. The core material was aged with 10% steam in air at 750 ℃ for 16 hours. Evaluation with typical H without preconditioning₂O and CO₂The concentration is carried out but no hydrocarbons and no carbon monoxide are present in the feed gas.

Table 11 below shows NO_xThe discharge amount is in g/Km.

TABLE 11

The results in Table 11 show that the catalysts with Pt (example 2) and Pt/Rh (example 4) removed more than 95% of the NH₃Emissions, while having Rh (example 5), Pt/Pd (example 6) and no PGM (example 1) resulted in high ammonia emissions. This indicates that no reduction in ammonia oxidation was achieved under the laboratory test conditions. The samples with Pt/Rh (example 4) were at low N₂O and NH₃High NO at discharge_xThe most preferred trade-off for conversion.

Reference throughout this specification to "one embodiment," "certain embodiments," "one or more embodiments," or "an embodiment" means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrases such as "in one or more embodiments," "in certain embodiments," "in one embodiment," or "in an embodiment" in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.

Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It will be apparent to those skilled in the art that various modifications and variations can be made in the method and apparatus of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims

1. A catalyst for oxidizing ammonia, the catalyst comprising:

a washcoat comprising copper on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms physically mixed with platinum and rhodium on a refractory metal oxide support comprising alumina, silica, zirconia, titania, physical mixtures thereof or chemical combinations including atom doping combinations thereof.

2. The catalyst of claim 1, wherein the washcoat is disposed on a monolithic substrate.

3. The catalyst of claim 2, wherein the monolithic substrate is a flow-through honeycomb substrate comprising a plurality of fine, parallel gas flow channels extending along a longitudinal axis of the substrate.

4. The catalyst of claim 1, wherein the catalyst comprises an amount of platinum and an amount of rhodium.

5. The catalyst of claim 2, wherein the catalyst comprises an amount of platinum and an amount of rhodium.

6. The catalyst of claim 3, wherein the catalyst comprises an amount of platinum and an amount of rhodium.

7. The catalyst of claim 4 wherein the amount of platinum is in the range of 0.3 to 20g/ft³Is present in an amount of 0.3 to 20g/ft³Is present and wherein no other platinum group metals are present.

8. The catalyst of claim 5, wherein the amount of platinum is in the range of 0.3 to 20g/ft³Is present in an amount of 0.3 to 20g/ft³Is present and wherein no other platinum group metals are present.

9. The catalyst of claim 6, wherein the amount of platinum is in the range of 0.3 to 20g/ft³Is present in an amount ofAt 0.3-20g/ft³Is present and wherein no other platinum group metals are present.

10. The catalyst of any one of claims 1-9, wherein the copper on the molecular sieve material is homogeneously mixed with the platinum and rhodium on the refractory metal oxide support in the washcoat.

11. The catalyst of any one of claims 1-9, wherein the copper on the molecular sieve material and the platinum and rhodium on the refractory metal oxide support are separated from each other and the platinum and rhodium on the refractory metal oxide support is physically mixed with the copper on the molecular sieve material.

12. The catalyst of claim 10, wherein the copper on the molecular sieve material and the platinum and rhodium on the refractory metal oxide support are separated from each other and the platinum and rhodium on the refractory metal oxide support are physically mixed with the copper on the molecular sieve material.

13. The catalyst of any one of claims 1-9, wherein the refractory metal oxide support is doped with a dopant selected from one or more of Ce, La, Ba, Zr, Hf, Ta, Mn, Si, Ti, W, Mo, and Re.

14. The catalyst of claim 12, wherein the refractory metal oxide support is doped with a dopant selected from one or more of Ce, La, Ba, Zr, Hf, Ta, Mn, Si, Ti, W, Mo, and Re.

15. The catalyst of any one of claims 1-9, wherein the washcoat is substantially free of copper aluminate.

16. The catalyst of claim 14, wherein the washcoat is substantially free of copper aluminate.

17. The catalyst of any one of claims 1-9, wherein the molecular sieve material is selected from the group consisting of framework types CHA, AEI, AFX, ERI, KFI, LEV, AFT, EAB, DDR, PAU, RHO, SAV, SAT, TSC, UEI, and combinations thereof.

18. The catalyst of claim 16, wherein the molecular sieve material is selected from the group consisting of framework types CHA, AEI, AFX, ERI, KFI, LEV, AFT, EAB, DDR, PAU, RHO, SAV, SAT, TSC, UEI, and combinations thereof.

19. The catalyst of any one of claims 1 to 9, wherein the molecular sieve material is a CHA framework type.

20. The catalyst of claim 18, wherein the molecular sieve material is a CHA framework type.

21. The catalyst of any one of claims 1-9, wherein the molecular sieve material has a silica to alumina ratio of 2-200.

22. The catalyst of claim 20, wherein the molecular sieve material has a silica to alumina ratio of 2 to 200.

23. A catalyst for oxidizing ammonia, the catalyst comprising:

a first washcoat zone containing copper on a small pore molecular sieve material having a maximum ring size of 8 tetrahedral atoms, wherein the first washcoat zone is substantially free of platinum group metals; and

a second washcoat zone containing the catalyst of claim 1.

24. The catalyst of claim 23, wherein the first washcoat zone and the second washcoat zone are disposed on a monolithic substrate.

25. The catalyst of claim 24, wherein the first washcoat zone and the second washcoat zone are disposed adjacent to each other on the monolithic substrate and the first washcoat zone is upstream of the second washcoat zone.

26. The catalyst of claim 23, wherein the second washcoat region is free of other platinum group metals.

27. The catalyst of claim 24, wherein the second washcoat region is free of other platinum group metals.

28. The catalyst of claim 25, wherein the second washcoat region is free of other platinum group metals.

29. The catalyst of any one of claims 23-28, wherein the molecular sieve material is selected from the group consisting of framework types CHA, AEI, AFX, ERI, KFI, LEV, AFT, EAB, DDR, PAU, RHO, SAV, SAT, TSC, UEI, and combinations thereof.

30. The catalyst of any one of claims 23 to 28, wherein the molecular sieve material is a CHA framework type.

31. The catalyst of claim 29, wherein the molecular sieve material is a CHA framework type.

32. The catalyst of any one of claims 23-28, wherein the molecular sieve material has a silica to alumina ratio of 2-200.

33. The catalyst of claim 31, wherein the molecular sieve material has a silica to alumina ratio of 2 to 200.

34. A method for treating emissions produced in an exhaust stream of a lean burn engine, the method comprising:

injection of ammonia or ammonia precursor into a gas containing NO_xCO or hydrocarbons; and passing the exhaust stream over the catalyst of any one of claims 1-33.

35. A system for treating emissions produced in an exhaust stream of a lean burn engine, the system comprising:

an ammonia source and an injector for injecting the ammonia source into the exhaust stream;

a selective catalytic reduction catalyst located downstream of the ammonia source to promote the reaction of ammonia with nitrogen oxides to selectively form nitrogen and H₂O; and

a catalyst according to any one of claims 1 to 33.

36. The system of claim 35, further comprising an ammonia oxidation (AMOx) catalyst.